The Salvador-Warts-Hippo (SWH) pathway was first discovered in Drosophila melanogaster as a potent inhibitor of tissue growth. The SWH pathway is highly conserved between D. melanogaster and mammals, both in function and in the mechanism of signal transduction. The mammalian SWH pathway limits tissue growth by inhibiting the nuclear access and expression of the transcriptional co-activator, Yes-associated protein (YAP). Mutation and altered expression of SWH pathway proteins has been observed in several types of human cancer, but the contribution of these events to tumorigenesis has been unclear. Here we show that YAP can enhance the transformed phenotype of ovarian cancer cell lines and that YAP confers resistance to chemotherapeutic agents that are commonly used to treat ovarian cancer. We find that high nuclear YAP expression correlates with poor patient prognosis in a cohort of 268 invasive epithelial ovarian cancer samples. Segregation by histotype shows that the correlation between nuclear YAP and poor survival is predominantly associated with clear cell tumors, independent of stage. Collectively our findings suggest that YAP derepression contributes to the genesis of ovarian clear cell carcinoma and that the SWH pathway is an attractive therapeutic target.

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Metastatic disease is the major cause of breast cancer related death and despite many advances, current therapies are rarely curative. Tumor cell migration and invasion require actin cytoskeletal reorganisation, to endow cells with capacity to disseminate and initiate the formation of secondary tumors. However, it is still unclear how these migratory cells colonise distant tissues to form macrometastases. The E6-associated protein, E6AP, acts both as an E3 ubiquitin-protein ligase and as a coactivator of steroid hormone receptors. We report that E6AP suppresses breast cancer invasiveness, colonisation and metastasis in mice and in breast cancer patients, loss of E6AP associates with poor prognosis, particularly for with basal breast cancer. E6AP regulates actin cytoskeletal remodelling via regulation of Rho-GTPases, acting as a negative regulator of ECT2, a GEF required for activation of Rho-GTPases. E6AP promotes ubiquitination and proteasomal degradation of ECT2 for which high expression predicts poor prognosis in breast cancer patients. We conclude that E6AP suppresses breast cancer metastasis by regulating actin cytoskeleton remodelling through the control of ECT2 and Rho-GTPase activity. These findings establish E6AP as a novel suppressor of metastasis and provide a compelling rationale for inhibition of ECT2 as a therapeutic approach for patients with metastatic breast cancer. Note: This abstract was not presented at the conference. Citation Format: Mariam Mansour, Sue Haupt, Ai-Leen Chan, Nathan Godde, Alexandra Rizzitelli, Sherene Loi, Franco Caramia, Siddartha Deb, Elena A. Takano, Mark Bishton, Cameron Johnstone, Yarra Levav-Cohen, Yong-Hui Jiang, Alpha S. Yap, Stephen Fox, Ora Bernard, Robin Anderson, Ygal Haupt. The E3-ligase E6AP represses breast cancer metastasis through regulation of ECT2-Rho-GTPases signaling. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr A72.

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